This invention relates to a device which is designed for use in a disk storage apparatus (e.g., a hard disk drive) having an MR head (including a GMR head) used as a read head, and which effectively removes noise from a read signal in the head amplifier circuit provided for amplifying signals read by the read head from a disk.
In a hard disk drive (HDD), the magnetic head reads data from, and writes data on, the recording surface of a disk. The disk is a magnetic recording medium which is rotated at high speed by a spindle motor. The head outputs the data read from the disk after converting the data into read signals which are electrical signals. A head amplifier circuit amplifies the read signals. The read signals thus amplified are transferred to a signal processing circuit generally known as "read channel." The read channel performs data processing such as converting the read signals to digital data. That is, the read channel reproduces the data from the disk.
As shown in FIG. 7, an HDD has a spindle motor 110, at least one disk 111 connected to the spindle motor 110, a head 112, a suspension 113 holding the head 112, an FPC (Flexible Printed Circuit) board 700, and a head amplifier circuit 600 and other circuit components, all mounted on the FPC board 700.
The head 112 is a read/write composite head comprising a read head for reading (data and a write head for writing data. The head 112 floats above the disk 111 due to the air stream generated while the spindle motor 110 rotates the disk 111 at high speed. While floating, the head 112 is moved in the radial direction of the disk 111 by a carriage 115 which is driven by a voice coil motor (VCM) 114. The carriage 115 is the main component of a head actuator and holds the suspension 113, which turn supports the head 112. A CPU (not shown), i.e., the main component of the HDD, controls the current which flows in the VCM 114 and the direction in which the current flows in the VCM 114. The head 112 is thereby moved to a target position on the disk 111 (i.e., a track to be accessed). At the target position the head 112 reads data from, or writes data on, the disk 111.
The read head of the head 112 is an MR head having an MR (Magnetoresistive) element or a GMR (Giant Magnetoresistive) element. Here it is assumed that the head 112 is a read head which is an MR head. As shown in FIG. 8, the head 112 has two output terminals 210a and 210b. The second output terminal 210b is connected to the ground.
The head amplifier circuit 600 amplifies a signal read by the head 112, hereinafter called "read signal." The head amplifier circuit 600 is an IC circuit known as "head IC." As shown in FIG. 8, the circuit 600 outputs the read signal to a read channel 800. The FPC board 700 is provided in a disk enclosure (DE) 118. The read channel, the CPU, a disk controller (HDC), and the like are mounted on a main CPB (Printed Circuit Board) 119. The main CPB 119 is located outside the DE 118 and connected to the FPC board 700 by a connector.
The top of the DE 118 is covered with a top cover 120. The top cover 120 is fastened by screws and thereby set in a fixed position. The DE 118 is therefore a sealed structure which allows no entry of dust.
The head 112 and the head amplifier circuit 600 are connected to each other by head lead (head wire) 122 and by wiring patterns formed on the FPC board 700 (see FIG. 8). One end of the FPC board 700 is fastened to the fixed part 116a of the carriage 115. In other words, the FPC-fastening part 116a connects the head 112 to the carriage 115. The other end of the FPC board 116 is fastened to the fixed part 116b of the base of the DE 118. The head amplifier circuit 600 is mounted on the fixed part 116b. The head amplifier circuit 600 can be mounted on the carriage 115 if the HDD is a 3.5-inch HDD. If the HDD is a smaller one, e.g., a 2.5-inch HDD, however, the circuit 600 cannot be mounted on the carriage 115. This is why the head amplifier circuit 600 is provided, usually on the fixed part 116b of the base of the DE 118.
The part of the FPC board 116 which exists between the fixed parts 116a and 116b is a movable part 116c. The movable part 116c is relatively long, several centimeters long. The wiring pattern (signal line) provided on the FPC board 700 is therefore several centimeters long. The wiring pattern connects the head 112 fastened by the carriage-side fixed part 116a and the head amplifier circuit 600 mounted on the base-side fixed part 116b.
Being so long, the wiring pattern absorbs the noise (external noise) generate(d from the electromagnetic waves and the like emanating from the devices located outside the HDD. The noise is probably superposed on the read signal supplied from the head 112 and is probably input to the head amplifier circuit 600.
The connection between the head 112 (MR head) and the head amplifier circuit 600, both incorporated in the HDD shown in FIG. 7, will be described with reference to FIG. 8.
Of the two output terminals of the head 112, the terminal 210a is connected to the input of the amplifier 601 (A1) provided in the head amplifier circuit 600, by the wiring pattern (conductor pattern) 211a formed on the FPC board 700. The other output terminal 210b of the head 112 is connected to the ground in the head amplifier circuit 600, by the wiring pattern (conductor pattern) 211b formed on the FPC board 700. Thus, the amplifier 601 (A1) provided in the circuit 600 is a single-end type amplifier.
The head amplifier circuit 600 incorporates a two-input differential amplifier 602 (A2). One input terminal of the differential amplifier 602 is connected to the output terminal of the amplifier 601 (A1). The other input terminal of the differential amplifier 602 is connected to the ground. The differential amplifier 602 converts the read signal amplified by the single-end type amplifier 601 to a differential signal, which is output to the read channel 800 mounted on the main PCB 119.
On the FPC board 700 connecting the head 112 and the head amplifier circuit 600, the noise (external noise) generated from the electromagnetic waves emanating from the devices located outside the HDD may be superposed from the patterns 211a and 211b onto the read signal. If so, the read signal containing the noise will be amplified and degraded in terms of quality. Such a low-quality read signal probably causes a read error in the hard disk controller (HDC) even if the read signal is subjected to noise-removing process in the read channel 800.
The noise can be removed from the read signal to be input to the head amplifier circuit 600 by using the technique disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 4-209304. This technique is to use an auxiliary element, a second amplifier and a third amplifier. The auxiliary element is provided on the slider, i.e., head body, and does not read data unlike the head 112 (i.e., main element) which reads and writes data. The auxiliary element detects an external noise signal. The second amplifier amplifies the external noise signal and inverts the phase thereof. The third amplifier superposes the output signal of the second amplifier on the read signal amplified by the first amplifier, canceling out the external noise only.
This known technique requires the auxiliary element provided on the slider (i.e., the head body). Furthermore, signal lines must be used to connect the auxiliary element to the second amplifier. It is extremely difficult to provide signal lines between such a magnetic head and the second amplifier. It is difficult to do so, particularly in an HDD which has a plurality of heads positioned one above another. To provide signal lines of this kind would increase the manufacturing cost of the HDD.
The known technique described above can remove the external noise from the read signal only if the head 112 has detected the noise. As the inventors hereof have found, most of the external noise contained in the read signal input to the head amplifier circuit 600 has been detected by the writing patterns provided on the FPC board 700 and connecting the head 112 to the circuit 600. This is probably because the wiring patterns 211a and 211b are as long as several centimeters in the HDD shown in FIG. 8.